Micro-Raman Scattering Analysis of Temperature-Dependent Electron Mobility and Fermi Level in n-Doped Homoepitaxial GaN Layers for Power Electronics

This work presents a temperature-dependent micro-Raman spectroscopy study (300-573 K) of homoepitaxial n-type GaN layers with different Si doping levels ranging from 10¹⁵ to a few 10¹⁸ cm⁻³, where the analysis of different vibrational modes enables simultaneous extraction of structural and electronic properties. The evolution of the E₂(high) mode and the associated phonon correlation length with doping and temperature reveal progressive lattice disorder, allowing static disorder related to dopant incorporation to be distinguished from dynamic disorder arising from phonon interactions. In parallel, the A₁(LO) mode highlights the Fano interaction between the discrete phonon and the electron continuum, where the asymmetry parameter provides access to the Fermi level EF position. At 300 K, the energy separation between the conduction band and EF decreases from ∼0.19 eV for the lightly doped sample to ∼0.03 eV for the heavily doped sample. At 573 K, this distance increases to ∼0.43 eV and ∼0.08 eV, respectively, reflecting the temperature-dependent shift of the chemical potential. These results confirm both efficient dopant activation and the transition toward quasi-degenerate behavior at high carrier concentrations. Finally, analysis of A₁(LO) phonon-plasmon coupling within the LPP model allows the determination of carrier mobility as a function of doping and temperature: at 300 K, the mobility decreases from 916 cm²/V·s in lightly doped samples to 355 cm²/V·s in heavily doped layers, with further reductions at elevated temperatures due to thermally activated scattering and carrier redistribution. These results demonstrate that Raman spectroscopy is a powerful nondestructive tool to simultaneously assess electronic transport properties and crystalline disorder in vertical GaN-based power electronics.